Maintenance of homeostatic immune surveillance and the development of protective immune responses require that leukocytes efficiently cross tissue barriers and traffic throughout the body, moving in and out of the bone marrow, lymphoid and non-lymphoid tissues under both normal and infected or inflamed conditions. As such, the direct observation of leukocyte adhesion, migration and communication in lymphoid and nonlymphoid tissues with microscopy is one of the most important experimental approaches. The Imaging Core (Core B) has been established based on a stated need of PPG investigators and is designed to draw on the considerable experience of its key personnel to provide expertise and specialized equipment in the design and execution of in vivo imaging studies of effector T cell functions in infected tissues. The main missions of the Imaging Core are as follows: 1. To provide state-of-the-art imaging capabilities in conducting specific experiments regarding intra- and extravascular leukocyte adhesion and migration as well as cell-cell interactions during local immune responses in as many as six dimensions (i.e. 3D-space, time, color, fluorescence signals (e.g. FRET, photoactivation, or photoconversion)). 2. To provide proper training and technical assistance in imaging acquisition and analysis of the collected image data. The core will provide computational resources for the storage, processing and in-depth analysis of digital and video-based imaging data. 3. To provide assistance in the planning of in vivo animal studies by offering standardized infectious/inflammation models and a custom-designed environment with appropriate biosafety conditions for the generation, housing and intravital microscopy analysis of live cell cultures, explanted tissues, and infected mice. 4. To maintain and improve existing capabilities and to develop new processing methodologies for the effective and timely completion of the proposed studies. The Imaging Core has already been highly effective in achieving some of these goals by providing effective service that both facilitates research and fosters collaborations between investigators, and by enabling development of novel in vivo animal models and imaging techniques.